The present invention relates to computer graphics. More specifically, the present invention relates to the use of multi-resolution texture pyramids for rendering images.
Three-dimensional scenes have become an important form of content that is deliverable through the Internet. Standard formats such as Virtual Reality Modeling Language (xe2x80x9cVRMLxe2x80x9d) make it possible to dynamically download complex scenes from a server directly to a web browser.
A scene may be rendered by downloading 3-D geometry objects from a server, forming a camera model from the geometry objects, and projecting the objects into the scene. The projections are filled in with pixels, and the pixels are shaded.
For greater realism the pixels may also be textured. A texture may be any form of discrete image (e.g., a scanned photograph). The texture adds detail to surfaces of the geometric objects without an increase in actual geometric data size or complexity. For example, a device-independent bitmap representing wood grain may be mapped onto the faces of a cube to make the cube look like a wooden box. The most commonly used form of texture map is a multiple resolution image pyramid or xe2x80x9cMIP map,xe2x80x9d which stores the texture in multiple levels of resolution.
The multi-level resolution pyramid allows different resolutions of objects in the scene to be downloaded. For example, if an object such as a cube is being viewed from a distance, it would appear small in a scene. Therefore, downloading the full resolution images of the faces of the cube would provide unnecessary detail. Instead, lower resolution images of the faces are downloaded as texture.
In a complex scene with many texture maps, the texture may represent a substantial percentage of the data that is downloaded, often exceeding the size of the object data. In some cases, such as VRML scenes used to display panoramas, the object data is almost incidental.
Limited bandwidth between server and client presents an obstacle to the availability of more complex scenes, since geometry and texture maps for a reasonably complex scene may take a relatively long time to transfer over a typical telephone modem link. The limited bandwidth can cause a bottleneck in the rendering of the scenes. Of course, the severity of the bottleneck will depend in part upon the amount of texture that is transmitted, the type of network and the speed of the network connections.
Faster network connections will not necessarily overcome the bandwidth problem. Even as connection speeds become faster, there will still be a desire to transmit even more texture and render even more complex, realistic images.
Therefore, it is an objective of the present invention to reduce the bandwidth requirements for the transmission of texture.
Bandwidth requirements are reduced by the present invention. According to one aspect of the present invention, a low resolution tile of a first multi-resolution texture pyramid is fetched from a remote site, a local multi-resolution texture pyramid is initially synthesized from the fetched low resolution tile, and a sequence of images are rendered while using the local pyramid to provide texture. The local pyramid is updated while the sequence of images is being rendered. The local pyramid is updated by fetching at least some higher resolution tiles of the first pyramid from the remote site and by replacing synthesized tiles in the local pyramid with corresponding tiles that have been fetched. The higher resolution tiles are fetched according to visibility in the scenes being rendered. The tiles having a higher visibility are fetched before the tiles having a lower visibility.
The fetching of the higher resolution tiles from the remote site is performed in parallel with the rendering of the image sequence. Thus, real texture in the image sequence is progressively increased as synthesized tiles in the local pyramid are selectively replaced with corresponding tiles that have been fetched from the remote site.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.